1. Field of the Invention
The invention refers to a device for the dosed release of an injectable product, wherein the driven member contains a driven bush surrounding the driven rod, which driven bush engages into the drive member and is displaced together with the driven rod, and a rear wall--in relation to the feed direction--of the container protrudes at least during a release into an annulus formed between the driven rod and the driven bush.
2. Description of the Related Art
Devices such as the invention are preferably devices for the injection or infusion of a liquid drug solution, preferably a liquid medication such as insulin or hormone preparation solutions. Particularly preferred are portable devices, especially in the form of so-called injection pens which hereinafter are also representative for other devices.
Known injection pens but also pump devices for the infusion or infusion/injection of drug solutions contain a housing in which a container containing the product can be accommodated in a specially provided retainer. Within this container, a piston is displaceably accommodated. When the piston is moved in a feed direction, a product dose is released as a result of the piston displacement. For this purpose, the container, generally an ampoule, is fixed in the retainer in such a way that a driven member of a drive means forces the piston to move in feed direction to release the product. The driven member contains a driven rod protruding into the container towards the piston if the container is contained in the housing. A drive member of the drive means makes contact with the driven member in such a way that by activating the drive member, the driven member can be displaced in feed direction. The drive means is preferably at least a single-stage spindle drive. In known injection pens with spindle drives, the drive member, preferably formed as a drive bush, is activated by rotation in order to dose the product dose to be released with the next injection and also by straight displacement in the feed direction of the piston, i.e. by manually exerted pressure. In known pump devices with spindle drives, the drive member is only activated by rotation. The rotation in turn causes a forward displacement of the driven member which in pump devices is generally directly transferred onto the piston.
In particular for a portable device which is carried by the user, the external dimensions of the device should be as small as possible. Of special significance is a reduction of the length of the means or device in the feed direction. As a result, either the entire means including the container containing the product can be made smaller or a longer container can be used if the overall length remains the same. The longer container may accommodate more product. The longer container could, however, also be a so-called double-chamber ampoule in which the product and a solution fluid are contained in two separate chambers arranged in series and are only mixed immediately before the first injection or infusion.